Telephone system



July 3, 1934. s zu 1,965,435

TELEPHONE SYSTEM Filed Feb. 23, 1933 INVEN TOR Y. SH/MA 2 U AT ORNEY Patented July 3, 1934 UNITED STATES PATENT OFFICE Japan, assignor to Western Electric Company, incorporated, New York, N. Y., a corporation of New York Application February 23, 1933, Serial No. 659,031

In Japan April 22, 1932 5 Claims.

This invention relates to telephone systems and. in particular to automatic telephone exchange systems in which a plurality of automatic oiiices are associated with a number of common trunk lines for communication between subscribers at the various ofiices.

An object of the invention is to obtain in automatic telephone exchange systems an economical arrangement of common trunk lines for intercommunication between offices.

I-Ier'etofore systems have been provided in which stations on common lines may be selectively called by means of impulses operating step-bystep' apparatus to select different positions. Systerns have also been provided at which intercommunication between stations over a common power line may be established between subscribers by selecting stations by impulses and communicating over the common power line.

A feature of the present system is an arrangement in which a number of trunks are common to a number of automatic exchanges in which normally there is connected a single line relay for each trunk at each exchange, in which when a subscriber at one exchange desires to establish a connection with a subscriber in another exchange, a source of current is connected at the call originating exchange for the transmission of impulses, while aiter the connection has been established this source is disconnected and in which when the talking connection has been established no other apparatus except the line relays are connected to the trunk used at any of the other exchanges.

Referring now to the drawing, Fig. 1 shows one example of an arrangement of a plurality of automatic telephone exchange offices and a common trunk line connecting said oilices.

. Fig. 2 shows diagrammatically the relation between the equipment at each automatic exchange as connected to a single common trunk line.

Fig. 3 shows in detail a common trunk line and the equipment associated therewith at one ofiice for calling by means of impulses a desired subscribers line in another ofiice and for establishing a connection to a desired subscribers line in this ohice. I

Referring now to the drawing in detail:

Fig. 1 shows in diagrammatic form a number of exchanges A, B, C, D, E and F connected together by common trunk lines.

Fig. 2 shows the equipment in one of these automatic telephone exchanges in diagrammatic form where the number of subscribers lines is less than one hundred for example; It shows a line finder 1 0, a local connector 11 and an incoming connector 12 with the means for establishing a connection to' a common trunlr line for incoming and outgoing calls indicated by a box 13. Such line finders andconnectors may be of any well known type. It may also be assumed that an ordinary step-by s'tep system is used in which the ninth level of the local connector 11 is employed as a selector for selecting an idle common trunk. For example, if a subscriber of line 14 desires to make an outgoing call, the line finder 1-0 will be operated when the subscriber removes his receiver from the switchhook in the usual manner and a connection will be established to a local connector 11. If an outgoing call number is then dialed, the first digit will advance the brushes ofthe connector 11 to the ninth level and the brushes will then hunt in the usual manner for an idle outgoingtrunle. Connections will then be established through the equipment 13 out over the trunk and when the subscriber dials the desired subscribers number at another exchange he will transmit series of impulses out over the trunk line to select the desired exchange and the desired subscribers line therein. The first series of outgoing impulses represents the exchange and the two succeeding series represent the desired subscribers number. The first series selects through an equipment suchas 13' the desired exchange and the two succeeding series operate an incoming connector such as 12 to complete the connection to the desired subscribers line and ring this subscriber the usual manner common the ste'p-by-step automatic art.

a Descriptionwill now be made of the operation of the system in connectionwith Fig. 3 which shows one ofthecommon trunk-lines 20' and the equipment atone exchange in sufiicient detail to afford a clear understanding of the detail of the present invention; One" set of terminals in the ninth-level of the connector 11 is shown at 21. 'To" these terminals connections may be established from calling subscribers inthe exchange for calls outgoing over the trunk line 20 to another exchange. A- selector switch 22 is shown that is individual to the trunk line 20 and through which connections may be made for incoming calls to this exchange oven the tip and ring conductors-shown at 23' that lead to the brushes of 'a'connec'tor such as 12' through which the connection maybe established toa desired subscriber in" this exchange. The selector'switch 22 is of the single movement rotary t'yp'e well known in the art} thestepping' magnet being shown at 24 and the brushesat 25 A description will now be made of the establishing of a connection out over trunk 20 from a calling subscriber in this exchange. The calling subscribers line will be connected through the line finder to a local connector when the subscriber lifts the receiver off the switchhook. The subscriber will then dial the numeral 9. This will advance the brushes of the connector to the ninth level where it hunts for an idle trunk. An idle set of terminals leading to an idle trunk 20 is indicated as stated at 21. If it is assumed then that the calling subscribers line has been connected to these terminals, relays A and D will be operated over the circuit completed through the tip and ring conductors. When relay D operates it connects ground to the ring lead and battery to the tip lead of the common trunk line 20. When relay A operates, it causes relays B and H to operate through contacts 111. When relay B is operated it connects ground to the sleeve terminal at 21 and thus makes the trunk line 20 busy to other calls and it also prepares a circuit which causes the relays F andH to operate and prepares a holding circuit for relay 0 when relay A is restored. When relay H is operated it changes over the contacts hl and hz and disconnects the line relay X from the trunk 20 and connects the trunk to the contacts d1 and 012 and hence the ground is connected to the ring conductor and battery to the tip conductor so that at the other exchanges the line relays X are all operated to establish selecting circuits for the operation of the exchange selecting switches 22. Relay C in the trunk is slow to operate and will, therefore, operate a short interval after the relay A so that the operating circuit for relay H is opened and this relay released. The battery and ground connections to the tip and ring conductors of trunk 20 are disconnected by the release of relay H. Relay X may be of the non-biased type in which the armature remains in the one position or the other by energization and when relay H removes battery and ground from the trunk the armatures of these relays remain in the position to which they were last operated.

Now when the calling subscriber dials a code number indicating the exchange desired, relays El and F are operated each time that relay A is restored. Relay D also operates and restores in unison with relay H. The battery and ground connections for the trunk 20 are therefore connected, but in reverse direction due to the switching of the contacts (11 and dz, thus causing the relays at all other exchanges to be operated accordingly. The operation at these exchanges will be described hereinafter. During the sending of this series of impulses relays B, H and F remain operated due to their slow to release characteristics.

When the dialing ceases relays H and F are restored and the tip and ring conductors are thereby connected for conversation to the trunk 20 through contacts hi, hz, f1, f2, 03, 04 to the calling subscribers line through condensers 27 and 28.

When the calling subscriber hangs up his receiver at the end of the conversation, relays A and D are restored and relay H is caused to operate by the restoring of relay A so that a ground ;changes are operated in the opposite direction to cause operation to take place to restore the circuits thereat to normal as will be described hereinafter. At the calling exchange relay B is restored a short interval after relay A and consequently also relays C, H and F so that the trunk 20 will be released for use for other calls.

A description will now be made of a call from some other exchange incoming over trunk 20 to select this exchange. In this case ground is connected to the ring conductor and battery to the tip conductor of the trunk 20 to operate relay X and thus cause relays G and J to operate which in turn causes relays E, F and K to operate. The arrangement is such that when relay F is operated it opens the talking circuit so that the pulsing will not interfere. When relay E is operated it makes this trunk 20 busy to the terminals at 21 and prepares a circuit for the holding of relay F operated when relay G is restored.

When relay K is operated, it prepares a circuit for receiving and selecting the exchange number. When the direction of current in the trunk line is changed by the dialing of the calling subscriber, relay X opens and closes its contacts and energizes relay L and the stepping magnet 24 in series each time relay J is restored, which causes the magnet 24 to step its brushes 25 to the terminals corresponding to the dialed number which is assumed to be number 3. Relay L is of the slow to release type and is maintained operated during dialing, thus holding the circuit for relay M opened during this period. As shown, this exchange is assumed to be selected by a single digit,

but arrangements could readily be made for using two digits by the use of a difierent stepping switch arrangement. When relay L is restored at the end of dialing relay M operates from ground at contact I03 and changes the connection over the circuit connected to the tip and ring conductors 23 which terminate in the connector such as 12. At the exchanges not called the operations are identical up to this stage. When the brushes of the switches at these exchanges corresponding to the switch 22 land on the third set of terminals, relays corresponding to relay Pare operated, and these relays cause the relays corresponding to relay Q to be maintained operated. Relays Q are slow to release and remain operated while the subscriber dials the next number. The equipments associated with the trunk 20 at these other exchanges are therefore held in this set condition until the call is terminated so that when the calling subscriber hangs up his receiver, the relays X are released to cause relays P and Q to restore, thus causing relays M to be restored. There is then established a self-interrupting circuit for the stepping magnets 24 in series with relays L and when the brushes of the switches are returned to normal position, this circuit is opened. While the relays L are operated, they hold the trunk line 20 in busy condition.

If, on the other hand, the exchange called is the exchange illustrated in Fig. 3, the brushes of switch 22 will land on the third set of terminals which are connected through leads 23 to a connector such as 12. In this case, relays M and N are operated. This causes relay F to be restored and establish the talking circuit through the condensers 2'7 and 28 from the calling exchange over trunk 20 through the contacts 111 and m. Now when the calling subscriber dials the number of the desired subscriber the connector 12 is operated to establish its connection in the usual manner. Although relay F is in its operated condition through the contacts g2 and ez while the calling subscriber is dialing, yet when the dialing is ended, relay F is restored by the operated condition of relays G and N so that the talking circuit is established at the end of the dialing and the calling subscriber will therefore hear a calling tone. When the called subscriber is rung in the usual manner and answered, conversation may take place.

When the calling subscriber hangs up his receiver at the end of the conversation, relays X open their contacts by current flowing in the opposite direction through the trunk as hereinbefore described so that the connector 12 will be restored and the selector 22 and all selectors at the other exchanges will restore in the usual manner as hereinbefore described.

While the present invention has been disclosed in connection with but a single system it should be understood that it could readily be embodied in a plurality of other similar systems without departing from the spirit thereof.

What is claimed is:

1. In a telephone system, a plurality of oflices, subscribers lines at said offices, a plurality of trunk lines connecting said offices, means operative at said oifices for establishing a connection between the subscribers lines in one office and a subscribers line in another ofiice over an idle trunk, a source of current at each oifice, a relay at each ofiice, said means operating to include the source of current at the call originating ofiice in the trunk used for the establishing of a connection during the establishing of said connection and operative to include the relays only in said trunk after the establishing of a connection.

2. In a telephone system, a plurality of ofiices, subscribers lines at said ofiices, common trunk lines connecting said oflices, means operative at said ofiices for establishing a connection between a subscribers line in one OfllCB and a desired subscribers line in another office over an idle common trunk line and for thereafter preventing other such connections from being established over this trunk line, said means including a direct current source connected to this trunk at the call originating ofiice during the establishing of said connection only and including a relay connected to this trunk at each oflice after said connection has been established.

3. In a telephone system, a plurality of oflices, a plurality of common trunk lines connecting said offices, subscribers lines at said ofiices, a line relay normally connected to each trunk at each oifice, a source of current associated with each trunk at each oflice but normally disconnected therefrom, means at a call originating office for seizing an idle trunk on an outgoing call including disconnecting the associated line relay and connecting the associated source of current to the seized trunk at said call originating office, means for transmitting series of impulses from said source over said seized trunk, means responsive to one series of impulses for selecting a desired ofiice and responsive to other series of impulses for selecting a desired line therein including the operation of the associated line relays, and means responsive when the desired subscribers line has been connected to the trunk for disconnecting the current source and reconnecting the line relay to the trunk at the call originating ofiice.

4. In a telephone system, a plurality of oflices, subscribers lines at said ofiices, common trunk lines connecting said oflices, a relay connected to each trunk at each office, a source of current associated with each trunk at each office, but normally disconnected therefrom, means operative at said ofiices for establishing a connection between a subscribers line in one office and a desired subscribers line in another oifice over an idle trunk line, means for preventing other such connections from being established over said trunk, means operative on an outgoing call at the call originating ofiice for disconnecting the relay from the trunk used and for connecting the source of current to the trunk used during the establishing of said connection.

5. In a telephone system, a plurality of ofiices, subscribers lines at said offices, common trunk lines connecting said offices, a relay in the trunk lines at each oflice, a source of current associated with each trunk line at each office, means operative at said ofiices for establishing a connection between a subscribers line in one office and a desired subscribers line in another Ofi'lCB over an idle trunk, means operative on an outgoing call at the call originating ofiice for disconnecting the relay from the trunk used and for connecting the source of current to the trunk used during the establishing of said connection, and means for reconnecting said relay and disconnecting said source of current from the trunk used after the call has been established.

YASUJIRO SHIMAZU. 

